1. Technical Field of the Invention
The present invention relates in general to the mobile communications field and, in particular, to a base station architecture for a new generation of mobile communications systems.
2. Description of Related Art
The architecture used for any conventional mobile communications base station (BS) is a channel-based structure. FIG. 1 is a block diagram of such a conventional channel-based mobile communications BS 10. Essentially, as illustrated in FIG. 1, BS 10 allocates one of the fixed channel resources 12a(Ch.1-M1)-12N(Ch.2-M2) for each call. The baseband section of each channel is used to handle all of the possible radio transmission services available for a call, and the radio frequency (RF) section of each channel includes all of the RF resources needed for the call. Each BS sector (1xe2x88x92N) includes the maximum number of channel resources that will be needed for that sector over a period of time. Each sector""s channel resources are combined for transmission and reception via a respective antenna subsystem (1xe2x88x92N).
A significant problem with the conventional channel-based structure described above is that it is limited to systems that provide relatively few different radio transmission services and the processing requirements for those different radio transmission services are virtually the same. However, in the rapidly expanding telecommunications field, numerous multimedia communication scenarios are being developed with a large number of different radio transmission services, with each such service having substantially different processing requirements. Consequently, from a purely statistical standpoint, there is a growing need for communications network operators to be able to provide all of the different radio transmission services for different users, and the appropriate capacity that will be needed for the different sectors involved.
For a conventional channel-based BS operating in a multimedia scenario with a fixed amount of resources allocated for each channel and sector, each BS channel will have to be equipped with the resources needed for the radio transmission service that imposes the highest requirement on that channel""s processing capability. Also, in a multimedia scenario, each conventional BS sector will have to be equipped with the maximum resources that will be needed over time. Consequently, in the future, conventional channel-based BS hardware will be unrealistically dimensioned and thus provide a maximum processing capability that will far exceed what can be adequately supported by any future radio air interface. Therefore, for most of a conventional BS""s operating time, a large portion of the BS""s hardware will be unnecessarily allocated but unused, which will significantly and unnecessarily increase the overall size and weight of the BS.
The air interface to be used for a so-called xe2x80x9cThird Generationxe2x80x9d mobile communications system, such as, for example, a Wideband Code Division Multiple Access (W-CDMA) system, imposes a whole new set of requirements for a BS architecture compared to those set forth in previous standards. See, for W-CDMA, the xe2x80x9cReport on FPLMTS Radio Transmission Technology Special Group (Round 2 Activity Report),xe2x80x9d Version E 1.2, January 1997, Association of Radio Industries and Businesses (ARIB), FPLMTS Study Committee, JAPAN. Essentially, the Base Transceiver Station (BTS) for a third generation mobile communications system will have to be capable of handling such different end user services as voice, circuit-switched data, and packet-switched data. Also, the BTS will have to capable of supporting a number of different user data rates. For example, a third generation BTS will have to support voice signals at an 8 kbps rate, circuit-switched data from 64 kbps to 384 kbps, and packet-switched data from approximately 1 kbps to 160 kbps.
Furthermore, for a third generation BTS, separate protocols (encoding schemes) will be used to map users to a number of physical channels characterized by a symbol rate. An optimized encoding scheme will be used for each of the channels for maximum efficiency. A description of these protocols can be found in available documentation for W-CDMA. Thus, in a W-CDMA system, the same BTS should be capable of supporting different physical channels with a range of symbol rates between 16 ksps to 1024 ksps, and also be capable of handling multiple spreading rates. In fact, in order for the BTS to be capable of supporting very high user data rates, it also may have to support a number of chip rates. A third generation BTS will also have to be capable of supporting such a network function as xe2x80x9csofterxe2x80x9d handover (a handover where diversity is gained from two or more sectors corresponding to one BTS).
A BTS structured in accordance with the present invention is divided into a plurality of functional units which enables the signal processing resources to be flexibly allocated and cost-effectively implemented in hardware. Flexible communications interfaces are created between the BTS units which allows the signal processing resources within the units to be used more efficiently. Essentially, the BTS hardware is dimensioned to statistically distribute the signal processing resources among the different radio transmission services available. Consequently, the allocated BTS hardware can be used more efficiently, which minimizes the overall size and weight of the base station.